1. Field of the Invention
The present invention relates to a method for producing carbonaceous anode material capable of intercalating or deintercalating light metal ions such as lithium ions, to a carbonaceous anode material obtained by the method, and to a non-aqueous electrolyte cell using such material.
2. Prior Art
Compact portable electronic products such as camcorders, personal handyphone systems, laptop computers, etc., have been developed with recent advance in electronic teclinology, and hence, the development of a compact and light-weight secondary battery having high energy density for use as a portable power source is strongly demanded.
Recently, non-aqueous electrolyte cells using light metals such as lithium, sodium, or aluminum as charge carriers are attracting attention and active study is made thereon as batteries which fulfill the above requirements, because they can achieve higher energy density when compared with nickel-cadmium or lead batteries.
However, when a light metal such as metallic lithium is used as it is for the anode of a non-aqueous electrolyte cell, metallic lithium does not always form a uniform precipitate on the surface of the anode during the charging process (i.e., the process of precipitating metallic lithium), but sometimes form a dendritic precipitate. When such dendrites are formed, they gradually grow with repeated recharging as to finally reach the cathode to possibly cause an internal short circuit.
Accordingly, to prevent such light metal dendrites from forming, it is proposed not to use the light metals directly for the anodes, but to use them as dopants in a material capable of being doped and dedoped therewith. Concerning lithium ions, in particular, lithium-ion non-aqueous electrolyte cells equipped with anodes made of carbonaceous materials capable of intercalating or deintercalating lithium ions, such as natural graphite, artificial graphite, or non-graphitizable carbon materials, and being intercalated with carbon dopants, are now practically available. Such non-aqueous electrolyte cells boast superior safety and reliability, because the formation of dendrites is suppressed by incorporating light metals in non-metallic states.